In current art, integrated circuits (ICs) are building blocks for most electronic circuitry. IC technology has grown from single transistor devices to an art wherein single ICs may have more than a million circuits. Similarly, operating frequencies of microcircuits have increased to 100 megahertz and more. This growth in IC density and speed has benefitted users through development of increasingly smaller, faster, more capable, and more portable electronic equipment.
Increased capability in integrated circuits, however, comes with an inherent disadvantage in that the denser and faster ICs operate hotter than less powerful ICs. ICs, like most other electrical devices, consume electrical power and dissipate much of the power as heat. Higher circuit densities and higher operating speeds cause an IC to consume greater amounts of power and dissipate greater amounts of heat. This phenomenon is particularly true for state-of-the-art microprocessor CPUs, which may dissipate 30 to 50 watts. Recent experience in using such microprocessor CPUs as the Intel Pentium.TM., for example, has emphasized the need for heat removal.
A particular problem with hot ICs is that electrical properties of silicon devices change appreciably with temperature. For proper operation and reasonable service life, waste heat must be removed to keep ICs and surrounding structure and devices within safe operating temperatures.
Mounting and assembly constraints under which ICs are typically utilized serve to exacerbate the problem of heat removal. A premier use of microprocessor ICs, for example, is as central processing units (CPUs) for personal computers. These microprocessor IC's are typically mounted to a motherboard and are surrounded, in the same enclosure, by a variety of components, such as a power supply, disk drives, disk controllers, basic input/output system (BIOS), random access memory (RAM), video display adapter, small computer system interfaces (SCSI), and other heat-generating components commonly found in personal computers.
In recognition of the problem of heat generated by ICs, high-powered microprocessor CPUs often are provided on a motherboard with a fan apparatus that draws in surrounding air, passes the air at relatively high velocity over surfaces of the CPU package, and expels heated air into the immediate surroundings, that is, the unused volume within the enclosure of the personal computer. Fans for this purpose are available commercially, and may be added by a user to microprocessor CPUs and other ICs. Such fan apparatus has proven successful in its immediate purpose, which is to cause the directly-effected IC to run cooler.
The solution of fan-cooling an IC such as a microprocessor CPU creates a new problem. Expelling heated air from a microprocessor IC into the immediate surroundings within an enclosure of a personal computer raises the ambient temperature in the computer enclosure, which risks effective operation and life of many surrounding components in the computer enclosure.
In tests performed on conventional computers in conjunction with the present invention, ambient temperature in a personal computer enclosure, having a high-powered microprocessor IC with a fan, was measured at about 20 degrees C. with the computer not operating. After a few minutes with the microprocessor CPU and its fan operating normally, the air temperature within the personal computer enclosure rose to over 44 degrees C.
What is clearly needed is a method and apparatus that keeps a microprocessor IC operating within a specified safe temperature range without raising the temperature of the volume of air within a personal computer enclosure.